(a) Field of the Invention
The present invention is concerned with an electromagnet type pickup device, and more particularly it pertains to a supporting means for supporting a cantilever in an electromagnet type pickup device.
(B) Description of the Prior Art
Among known electromagnet type pickup devices, those which have been put to practice widely are divided roughly into the two types: those of the moving magnet type as shown in FIG. 1, and those of the induced magnet type as shown in FIG. 2. Referring to FIGS. 1 and 2, a pickup structure comprises a stylus 1, a cantilever 2 for transmitting the vibrations detected by the stylus 1, a permanent magnet 3 for converting the mechanical vibrations into variations of magnetic flux, and a spacer 4 for supporting a vibrating assembly which is comprised of the stylus 1, the cantilever 2 and the premanent magnet 3, or a vibrating metallic element 7. The spacer 4 is formed of an elastic material for damping this vibrating assembly. Numeral 5 represents a yoke for detecting the vibrations of magnetic flux produced by the vibration of the vibrating element. Numeral 6 represents a coil wound around the yoke 5.
The pickup device having the aforesaid arrangement is simple in structure and is easy to manufacture as will be understood from FIGS. 1 and 2. In the arrangement of pickup device shown in FIG. 1, the cantilever 2 is secured through a spacer 4 to the yoke 5 directly or through a pole piece. Accordingly, when the permanent magnet 3 is put into vibration, it will be understood that, because of the fact that the frequency of the vibration extends in a wide range, the spacer 4 becomes deformed as shown in FIGS. 3 to 5, leading to the prominent drawback that the fulcrum of vibration becomes unstable. In FIGS. 3 to 5, numeral 7 is a tubular member for facilitating the replacement of the vibrating member.
In the reproduction of a stereophonic record disk, the vibrating element is subjected to vibrations in all directions relative to the fulcrum of vibration. Thus, the unstable movement, in the form of wave, of the fulcrum of vibration has been the cause of markedly deteriorating various characteristics such as localization characteristic of sound image, frequency characteristic, linearity characteristic and cross-talk characteristic, of the pickup device. Such deterioration has constituted a big problem especially in the reproduction of the recorded information in a high frequency band.
A further drawback of the known pickup device is noted in that, since the vibrating element, during operation, is continuously pulled in the direction of running sound groove due to the friction between the tip of the stylus and the sound groove of the disk, the fulcrum of vibration which is comprised of an elastic spacer 4 will be formed to move forwardly during the play and to move rearwardly when the play is brought to a halt. This friction which is developed between the sound groove and the stylus varies its magnitude according to the cut shape of the groove, i.e. modulated by the sound signal, and will induce back-and-forth vibrations of the vibrating element which is not only unnecessary but also harmful to the generation of electric signals required for the reproduction of a musical sound. This plus the previously mentioned unstable fulcrum of vibration further aggravate the desired various characteristics mentioned above. In order to eliminate the above-stated drawbacks of the prior art shown in FIGS. 1 and 2, there has been proposed an arrangement that a tension wire 8 is secured to a permanent magnet 3 to retain and prevent the permanent magnet 3 from being driven in the direction of run of the sound groove, as shown in FIGS. 6 and 7. A pickup device of this type has the drawbacks that the strength of fixation between the wire and magnet is not enough and also that the fulcrum of vibration of the permanent magnet 3 may move to a considerable extent toward the supporting wire 8 side in accordance with the vibrations of this permanent magnet 3. The tension wire 8 is either bonded under tension to the cantilever 2 or secured thereto under tension by caulking as shown in FIGS. 6 and 7. However, the bonding, under tension, of the supporting wire to an extremely limited area is difficult so that there arises a deficiency in mechanical strength. On the other hand, the tension wire could break at the site where it is caulked or there could arise an insufficient mechanical strength. As such, this prior technique is not desirable from the viewpoint of function of the pickup device.
As a means of clearly defining the portion which acts as the fulcrum and of eliminating the aforesaid drawbacks caused by the tension wire, there have been proposed an arrangement using a piano string inserted within the spacer, and an arrangement comprising a pair of spacer members: a relatively hard one and a relatively soft one, the hard one being disposed in the central portion and surrounded by the soft one. These arrangements have been put to practice, but they lack reliability and besides they have a further drawback that their constructions are complicated.